Protective control circuit and apparatus



Feb. 7, 1939- J. R. ZWICKL I PROTECTIVE CONTROL CIRCUIT AND APPARATUS Filed-Sept. 27, 1955 2 SheejLs-Sheet 1 INVENTOR Feb. 7, 1939. v J, R zw c v 2,145,909

PROTECTIVE CONTROL CIRCUIT AND APPARATUS Filed Sept. 27, 1955 2 Sheets-Sheet 2 Fan Mnfar Coniro/ fit: Phase fian ressa Molar INVENTOR J2 Z W/c/r/ 501 phase Com 9mm Malar- Patented Feb. 7, 1939 UNITED STATES 2,145.00 rao'mc'nvn corrmoi. cmcm'r mm'rus Joesph B. Zwlckl, Philadelphia, Pa., casino: to Baldwin-Southwark Corporation, a corporation of Delaware Application September 27, 1935, Serial No. 42,492

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This invention relates generally to air conditioning apparatus of the type employing a compression refrigerating system having an aircooled condenser and the invention relates more particularly to an improved control circuit for the compressor and the condenser blower motor.

It is an object of my invention to provide in air conditioning apparatus an improved control system in which the elements are so arranged in combination with each other that the compressor motor is effectively disconnected in the event of partial failure of the compressor circuit, such as failure of one phase of a multiphase circuit, and is also protected against abnormal loading which may be caused by improper condenser operation such as failure of the blower motor. It is a further object to accomplish the foregoing desirable object in a manner which is economical in construction, maintenance and operation, and yet is simple, positive and foolproof whereby the apparatus may be placed in thehands of an inexperienced user with utmost safety to the apparatus and to the user in operating the same.

Other objects and advantages will be more apparent to those skilled in the art from the following description of the-following drawings in which:

Fig. 1 is a diagrammatic outline of a refrigerating system in which my improved control may be embodied;

Fig. 2 is a wiringdiagram showing my improved circuit and control for a single phase compressor motor;

Fig. 3 is a modification of 2 but showing the application of my invention to a three-phase compressor motor;

Fig. 4 is a wiring diagram of a modification for a two-phase compressor motor;

Fig. 5 is a wiring diagram for a single phase compressor similar to that shown in Fig. 2 but embodying a modified form of pilot circuit control.

In the particular embodiments of the inventon which are disclosed herein merely for the purpose of illustrating certain specific forms among possible others that the invention might take in practice, I have shown in Fig. 1 a diagrammatic arrangement of a refrigerating system having a compressor i, a condenser 2 and evaporator 3 all suitably connected in any usual manner to provide a compressor-condenser-evaporator circuit. The condenser is preferably cooled by outside air circulated by a blower 4 through a passage 5. Room air is circulated by a blower 8 through a passage I. It is of course understood that the apparatus as described is embodied in a unit suitable for location in a room or other enclosure as may be desired, although the inventlon is applicable to any refrigerating system where the component elements thereof are located for remote use. The blowers 4 and 6 are suitably driven by power means specifically shown as a common motor I I. The arrangement of the main circuits for the blower and compressor motors and the pilot circuit therefor will be more readily understood by the following description of their operation.

To start the refrigerating unit, switch It, Fig. 2, is closed thereby supplying current to fan motor II from the main lines l2 and energizing the primary coil of a transformer". Upon closure of a compressor switch ll, a pilot circuit is energized from the secondary coil I! of transformer l3 provided that a thermostat or other auxiliary control device diagrammatically-indicated at I 6 is closed. The closure of the pilot circuit causes a solenoid l1 therein to be energized and thus close main contactors I 8 which supply current from main line 12 to compressor motor l9. Any suitable type of overload relays may be used to control the pilot circuit in accordance with the main compressor current, one such relay being diagrammatically indicated as including current coils 20 for operating switches 2! in the pilot circuit.

From the foregoing disclosure it is seen that if the fan motor circuit is opened or fails for any reason, such as by burning out of the fan motor or the blowing out of any usual fuses 22, then transformer I3 is deenergized and thus the pilot circuit is no longer supplied with current through its secondary coil IS with the result that compressor contacts are opened as by gravity or a spring 23. Thus an extremely simple arrangement has been provided for insuring complete protection of an air conditioning apparatus in case of failure of the fan motor circuit. Without this arrangement, the compressor would continue to operate upon failure of the fan circuit thus resulting in high condenser pressure with consequent danger of overloading the compressor mo tor. However, as long as the circuits are operative, a positive and yet simple means is afforded for insuring operation of the various refrigerating elements. A further advantage of this arrangement is that the transformer II can be a step-down transformer to permit a relatively low voltage in the pilot circuit with consequent safety to a user as well as lower installation costs.

above mentioned. The third phase 24 of the main supply wires is connected to the compressor by wire 25. To insure adequate protection of the compressor motor in case this phase, but no other, should fail due to blowing out cf-a fuse 26 or other cause, I have provided improved means for shutting down the compressor and' thus avoiding continued operation thereof on the remaining phase. Such continued operation would result in overload of this phase with consequent burning out of the compressor motor. To accomplish this, a relay 21 is connected to wire and to one of the wires such as- 28 of the fan motor circuit, preferably at a point after fuses 22. Relay coil 21 controls contacts 29 which are normally open by gravity or by a spring 30 when the apparatus is shut down. However, upon energization of the fan motor circuit by closure of switch i0, relay coil 21 will then be energized, thus closing contacts 28 to providev a closed pilot circuit.

In operation of the Fig. 3 modification, if it is assumed that fuse 28 should blow out, then there is maintained through relay coil 21 a feed-back circuit from wire 28 and thence through coil 21. across motor windings 3i and 32, wire 33 and' back to wire 28. However, the voltage in this feed-back circuit is materially less than normal voltage, and hence coil 21. is not of suflicient strength to hold contacts 2! closed against the action of spring 30. Itwill be understood that coil 21 is designed to close contacts 29 only when the coil voltage is above feed-back voltage. Whencontacts 29- open, then the pilot circuit is deenergized, thus opening main contactors l8 and stopping operation of the compressor motor.

In Fig. 4, circuits are provided for a two-phase motor. The fan motor circuit and transformer iii are identical to Figs. 2 and 3, these being supplied from onephase B. The pilot circuit is identical to that of Fig. 3 except that-switch 35, corresponding 'to switch .28, is operated by the other phase A. Afurther difference over Fig. -3 is. that each phase is carried through the main contactor i8, one phase being connected thereto by wires 36 and 31 to one of the compressor motor windings while the other phase is connected by wires 39 and 40 to the other phase winding of the compressor motor, the two motor windings then being connected to the other side of their respective phases bywi'res 42 and 43. In opera-v tion, if one or the other of fuses 44 in phase A should blow out, then relay coil 46 is deenergized to permit opening of contacts 35 by gravity or by a spring 45, thereby opening the pilot circuit with consequent deenergization of solenoid 23 and opening of main contact ll. Inasmuch as contacts i8 control bothphases as above described, it is seen that the compressor motor will 7 be completelydisconnected. In the event that one or the other of fuses 41 or 22 of phase B should blow out, then transformer l3 and the pilot circuit are deenergized with the result that main contacts i8 open. The overload relays 20 and their contacts 2| willnormally remain closed.

A common feature between Figs. 2, 3 and 4 is that the pilot circuit in all forms is controlled by the transformer current which is taken from a single phase of the main line. The transformpressure.

er arrangement has the further advantage of being free of contacts or mechanical links or cir-- cult breakers with the result that the pilot circuit cannot possibly be maintained closed by sticking contacts or other mechanical contrivances. Figs. 3 and 4 have the further common feature that the pilot circuit protects the compressor motor for the phase or phases which do not supply the current to energize the pilot circuit.

In Fig. 5, I have shown a modification wherein the pilot circuitis controlled by a relay 49 placed in series in the fan motor circuit for controlling contacts 50 of the pilot circuit. In operation of this device, if any part of the fan motor circuit should fail, then coil 49 will be deenergized with the result that the pilot circuit will open. Deenergization of the pilot circuit will open the main contactors l8 of the compressor motor circuit.-

Hence it will be impossible for the compressor motor to operate without operation of the fan motor. The transformer controls shown in Figs.

pressor motor system. The accomplishment of this result in a simple, economical and positive manner is highly desirable as it avoids possibility of the blower becoming inoperative while the compressor continues to operate, thus preventing the compressor from building up an excess head My improved arrangement also permits a relatively low voltage for the pilot circuit thereby affording a greater degree of safety in" the installation and operation of the'unit.

It will of course be understood that various changes in details of construction and arrangement of parts may be made by those skilled in the art without departing from the spirit of the invention as set forth in the appended claims.

I claim:

1. In combination, a refrigerating system having a compressor motor and motor driven means for circulating a cooling medium over a condenser, a pair of circuits one for supplying current to the compressor motor and the other for supplying current to said circulating motor, a pilot circuit adapted to open or close said compressor motor circuit, and means for controlling said pilot circult by said circulating motor circuit, the circuits being so arranged that the circulating motor is required, before the pilot circuit is conditioned to close said compressor-motor circuit, to be fully energized and thereby compel circulation of a cooling medium over the condenser to minimize the presence ofba'ck pressure upon starting of the compressor.

2. In combination, a refrigerating system having a compressor motor and motor driven means for circulating a cooling medium over a con- I denser," a pair of circuits one for supplying current to the compressor motor and the other for supplying current to said circulating motor; a pilot circuit adapted when energized to open or close said compressor motor circuit, and means energized by current in the circulating motor circuit for effecting energization of said pilot circuit.the circuitsbsingsoarrangedthatthe circulating motor is required. before the pilot circuit is conditioned to clou said compressor-motor circuit, to be fully energized and thereby compel circulation of a cooling medium over the con-' denser to minimize the presence of back pressure upon starting of the compressor.

3. In combination, a refrigerating system having a compressor motor and motor driven means for circulating a cooling medium over a condenser, a pair of circuits one for supplying current to the compressor motor and the other for supplying current to said circulating motor, a pilot circuit adapted to open or close said compressor motor circuit, and a transformer havins its primary coil energized by said circulating mo-. tor circuit and its secondary coil connected into said pilot circuit for supplying an induced current thereto, the circuits being so arranged that the circulating motor is required, before the pilot circuit is conditioned to close said compressormotor circuit, to be fully energized and thereby compel circulation of a cooling medium over the condenser to minimize the presence of back pressure upon starting of the compressor.

4. The combination set forth in claim 1 further characterized in that the compressor motor circuit has a solenoid operated switch whose solenoid is energized by the pilotcircuit.

5. The combination set forth in claim 1 further characterized in that the compressor motor circuit has a solenoid operated switch whose solenoid is energized by the pilot circuit, an overload switch forming a part of thepilot circuit, and an overload relay in said compressor motor circuit for wntrolling said overload switch.

8. In combination, a refrigerating system having a multi-phase compressor motor and a motor for circulating a condenser cooling medium, a circuit for said circulating motor, a multi-phase circuit for said compressor motor, a pilot control circuit for opening and closing said compressor circuit, said pilot circuit and circulating motor circuit being so arranged that the circulatin motor is required, before the pilot circuit is conditioned to close said motor-compressor circuit, to be fully energized and thereby compel circulation of a cooling mediumover the condenser to minimize the presence of back pressure upon starting of the compressor, and means in said control circuit adapted automatically upon faihire of any phase of the compressor circuitto open all phases thereof.

a I. In combination, a refrigerating system having a multi-phase compressor motor and a motor for circulating a condenser cooling medium, a multi-phase circuit for said compressor motor, a circuit for said circulating motor, a pilot circuit for opening and closing said compressor circuit, said pilot circuit and cirmilatlng motor circuit beingso arranged that the circulaisng motor is required, before the pilot circuit is conditioned to close said motor-compressor circuit, to be fully energized and thereby compel circulation of a cooling medium over the condenser to minimize the presence of back pressure upon starting of the compressor, a main switch operated by said pilot circuit for controlling certain phases of said compressor motor circuit while another phase .is continuously connected to the compressor motor, and means for opening said main switch automatically upon failure of said continuously connected phase.

8. In combination, a refrigerating system having a multi-phase compressor motor and a motor for circulating a condenser cooling medium, a multi-phase circuit for said compressor motor, a circuit for said circulating motor, a pilot circuit for opening and closing said compressor circuit, said pilot circuit and circulating motor circuit being so arranged that the circulating motor is required, before the pilot circuit is conditioned to close said motor-compressor circuit, to be fully energized and thereby compel circulation of a cooling medium over the condenser to minimize the presence of back pressure upon starting of the compressor, a main switch operated by said pilot circuit for controlling certain phases of said compressor motor circuit while another phase is continuously connected to the compressor motor, and means adapted upon failure of said continuously connected phase to open said main switch by a feed-back circuit through a portion of the circuit which is normally continuously connected.

9. In combinatioma refrigerating system having a two-phase compressor motor and motordriven means for circulating a cooling medium around a condenser, a circuit for the circulating motor, a two-phase circuit for the compressor motor, a pilot control circuit for said compressor circuit, a main switch controlling both phases of said compressor motor circuit, means energized by said control circuit for controllin said switch, means for controlling said control circuit by one of said phases, and means for also controlling said control circuit by the other of said phases whereby upon failure of either of said phases said control circuit effects opening of said main switch, said pilot circuit and circulating motor circuit being so arranged that the circulating motor is required, before the pilot circuit is conditioned to close said motor-compressor circuit, to be fully energized and thereby compel circulation of a cooling medium over the condenser to'rrinimize the presence of baclcpressure upon starting of the compressor.

JOSEPH R. ZWICHJ. 

